This project is a continuation of studies of various immunobiological properties of murine intestinal intraepithelial lymphocytes (IEL), so as gain a better understanding of human IEL in immunity and disease. There are three major components. The first involves detailed studies of IEL ontogeny and thymus dependency using adult Fl --> parent athymic radiation chimeras. Experiments in athymic chimeras will evaluate the status, and expression, of T cell receptor (TCR) genes using the method of polymerase chain reaction to determine the location(s) (e.g., intestinal vs extraintestinal), and nature, of extrathymically-matured IEL; and to characterize TCR variable region usage(s). Early-lineage origins of BM-- derived IEL precursors will be studied in IEL repopulation experiments. The functional nature, and phenotypic properties, of endogenously (in situ) activated IEL, and the degree of antigen recognition and specificity of effector IEL will be studied in athymic chimeras. A second series of experiments, in thymus-bearing mice, will examine functionally-important phenotypically-defined IEL to determine how such components may be mechanistically important. Newly-described IEL subsets will be studied for immunoregulatory and/or effector properties. IEL expressing the gamma-delta TCR will be studied for antigen specificity, cytotoxic activity, and as a function of antigen exposure in normal and germ-free mice. IEL-specific monoclonal antibodies isolated in this laboratory will be used to delineate functionally- and/or developmentally-relevant IEL. The third series of experiments will explore the relationship of IEL with and intestinal epithelia as they relate to IEL development and immune function. These studies will examine intestinal MHC class I and II antigens, using in vivo blocking experiments with non-depleting monoclonal antibodies, to evaluate the role of MHC in IEL development or effector activation. Intestine-derived epithelial cell lines will be isolated for in vitro experiments of IEL immunoregulation. Known epithelium-derived cytokines (e.g., TGFbeta(1), and others) will be used in studies of early- and late-stage IEL maturation and regulation.